1. Field of the Invention
The present invention generally relates to ultrasound phased arrays. More specifically, the invention relates to the architecture of the electronic system used to drive the array of the phased array system. While ultrasound phased arrays are applicable to therapeutic applications, including non-invasive surgery, laproscopic surgery, non-invasive cardiac ablation, drug delivery, drug activation and hyperthermia cancer therapy, it will be readily appreciated by persons skilled in ultrasound phased array technology that alternative and additional applications are well within the purview of this invention.
2. Description of the Prior Art
The construction and operation of ultrasound phased arrays is generally well known. Their construction typically includes a series of transducer elements supported on a curved or flat substrate. In order to drive the transducer elements, prior systems have included an individual drive amplifier for each transducer element. This approach is reasonable for a relatively small array, one without too many elements, such as a 32 element array. Large aperture ultrasonic arrays of today, however, have a much greater number of transducer elements, often requiring over a thousand elements. While the increased element count can result in greater flexibility in terms of forming a high quality, focused beam, it also can and does result in other drawbacks and limitations.
One major drawback associated with these large aperture arrays is the cost. The cost of the prior systems is directly related to the number of channels used in the system since each channel requires its own drive amplifier, drive cable, matching circuit, in addition to a transducer element and other components. Obviously, with an increased number of elements there is an increased number of amplifiers, etc. and a corresponding increase in, not only the cost, but also the size of the array and the system itself. As the size of the system increases, portability becomes compromised. The many cords, cables, coax and other transmission lines result in large bundles and a significant number of expensive specialized connectors. Since the bundles are mechanically stiff, the array itself (that part of the system which must be close to the patient) is difficult to move and to adjust for individual applications. This is particularly difficult for laproscopic arrays meant to operate inside the body and which are inserted via a small incision.
While array sizes have gotten larger, the size of the transducer elements has gotten smaller. With this reduction in element size there has also been a corresponding increase in the impedance of the systems. This has in turn required larger and more inefficient matching circuits, further increasing in size and cost while decreasing efficiency.
The high channel count (one amplifier and element per channel) of prior ultrasound phased array systems has often required that an economic tradeoff be made in the amplifier design. To reduce costs per channel, the amplifiers can be packaged on a circuit board, for example, sixteen (16) amplifiers per circuit board. In a large element array, for example, one having 1024 elements and an equal number of coax cables, the total number of amplifier circuit boards and matching network circuit boards would be the number of elements divided by the number of amplifiers per circuit board. For the above illustrative examples, the number of amplifier circuit boards and matching network circuit boards would be 64 each.
In the known system, each amplifier generates a "square wave" drive signal and, as a whole, the drive signals are only partially filtered by the matching networks. This results in harmonic rich signals on the drive cables. While it is possible to provide the amplifier circuit boards and the matching network circuit boards with coax and shielded RF boxes, this further adds to the overall bulk and expense of the system. Without the shielding, however, radiation from the RF energy is likely to be present in an amount that is unacceptable to the FCC and the actual end use environment, such as a hospital.
In view of the foregoing limitations and shortcomings of the prior art devices, as well as other disadvantages not specifically mentioned above, it should be apparent that there exists a need for an improved, large aperture ultrasound phased array system.
It is therefore a primary object of this invention to fulfill that need by providing an ultrasound phased array system having an improved architecture for driving the array.
Another object of this invention is to reduce the overall component count of the phased array without reducing the number of transducer elements. This includes reducing the number of drive amplifiers, cables, and associated hardware required to drive the elements. One feature of the present invention is that multiple transducer elements are driven by a common amplifier, thereby reducing the number of drive channels required for the array.
This invention also has as one of its objects providing an ultrasound phased array with reduced bulk and cost.
Still another object of this invention is to provide a drive system which allows signals to be passed both to and from the transducer elements thereby allowing the transducer elements to also be used as receivers.
Still another object of this invention is to provide a drive architecture which allows each amplifier to see an enlarged "effective" transducer element size having a lower impedance and which is therefore easier to electrically match.